1. Field of the Invention
The present invention relates to a semiconductor device having first and second conducting layers facing each other with an insulating layer interposed therebetween, and to a method of manufacturing the same.
2. Description of the Related Art
Hitherto, as memory devices of information processing apparatuses, magnetic disk devices have been widely used. However, the magnetic disk devices have the following drawbacks. First, they are easily affected by shock because they have a highly precise mechanical driving means. Second, the magnetic disk devices cannot access a storage media at a high speed because their access means to the storage media is mechanical one.
Recently, as the memory device of an information processing apparatus, the development of semiconductor memory devices has been made. The semiconductor memory devices do not have a mechanical driving means. Therefore, they have a high shock resistance and a high access speed.
Now, in an EEPROM (Electrically Erasable Programmable Read Only Memory), one of nonvolatile semiconductor memory devices, polycrystalline silicon doped with impurities having 3 or 5 valences is used as a material for floating gate electrodes and control gate electrodes, in consideration of productivity and stability of the interface between the gate electrodes and an underlying insulating film in a high-temperature heat treatment step performed later in a manufacturing process.
However, in the case where the polycrystalline silicon film is used as a floating gate, the following problem is accompanied. That is, as an insulating film between gate electrodes (a floating gate electrode and a control gate electrode) is decreased in thickness, the defect density of the insulating film between the gate electrodes increases. This problem constitutes a bar to miniaturization (high integration) of EEPROM and operation of EEPROM at low voltage.
To solve the problem, it is considered to use a single crystalline silicon film as a floating gate electrode. As a method of forming the single crystalline silicon film, known is the one disclosed in Jpn. Pat. Appln. KOKAI Publication No. 3-196673 in which an amorphous silicon film is crystallized into a single crystalline silicon film.
In this method, at first, a seed region for single crystallization is first formed. Second, on the seed region, an amorphous silicon film is deposited. Third, to the amorphous silicon film, impurities are doped by an ion implantation method and the like. Finally, the amorphous silicon film is crystallized into a single crystalline film by a solid phase growth of the lateral direction or by laser annealing.
However, this method requires additional steps such as a seed region formation step, an annealing step for crystallization, unlike the case where a polycrystalline silicon film is employed as a floating gate electrode. Therefore, this method is complicated in manufacturing steps.